The present invention relates to electroluminescent devices, and more particularly, to light-emitting devices based on small organic molecules.
Organic light-emitting diodes (OLED""s) have the potential for providing inexpensive alternatives to LED""s. OLED""s may be fabricated by coating the appropriate surfaces with the organic material either from solution or by using conventional vacuum deposition techniques, and hence, do not require the use of high cost fabrication systems such as those utilized in the fabrication of semiconductor devices. A simple OLED may be constructed from an electroluminescent layer sandwiched between an electron injection electrode and a hole injection electrode. More complicated devices utilize electron and hole transport layers between the above mentioned electrodes and the electroluminescent layer.
Addressable color displays may be constructed from OLED""s if individual OLED""s having three primary colors can be constructed. However, compounds having a common chemical structure that can be modified with a dye to provide the primary colors and which have sufficient quantum efficiency at low operating voltages have been lacking.
Broadly, it is the object of the present invention to provide an improved OLED.
It is a further object of the present invention to provide a set of OLED""s that can be utilized in constructing a color display.
It is a still further object of the present invention to provide an OLED that has higher quantum efficiency at low operating voltages than prior art OLED""s.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
The present invention is an organic LED having a cathode formed from a first conducting layer, an electroluminescent layer including an oxadiazole, thiadiazole or triazole compound, and an anode constructed from a second conducting layer which is transparent to light generated by the electroluminescent layer. In one embodiment, an electron transport layer is sandwiched between the anode and electroluminescent layers. Other embodiments utilize a hole transport layer between the electroluminescent layer and the anode either with or without the electron transport layer. In one embodiment, the anode is constructed from a layer of indium tin oxide and a layer of a hole transport material that bonds to indium tin oxide and which has an energy band intermediate between that of indium tin oxide and that of the hole transport layer.